No, depending on how you block it sub-domains of mail.google.com may be blocked, but not sibling domains.
If you blocked
*.google.com
then it would block mail.google.com and
www.google.comThere are basically 2 ways to block domains.
1. In a data list, where you use * and ? as wild-card matches, so you'd block a domain and sub-domains like
*.google.com
google.com
Data lists can be used via web access control rules as well directly, as well as by manual classifier rules.
2. In a web access rule, where you specify a site and in that case if you enter google.com, and select "include child items" then it will block google.com and any sub-domain
Adrien